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October 25, 2001

Canadian Jacks

The jack mackerel can be caught both inshore and offshore.

Q: While fishing off the central British Columbia coast during a mild El Niqo summer a few years ago, I caught this fish -- about 3 pounds and 18 inches long -- on a small metal jig. At first glance, I thought I'd caught a huge Pacific mackerel, but then I saw that it hasn't got the Pacific mackerel's finlets or characteristic dorsal pattern. So what is it, and is it a rare fish in these parts? - Dwayne Obbish, Vancouver, British Columbia

A: Although the Pacific or chub mackerel (Scomber japonicus) grows to more than 6 pounds and 25 inches, as you observe, it has about five small finlets in front of the tail, above and below, which your fish lacks. What you caught appears to be a member of the jack family, the jack mackerel (Trachurus symmetricus), which lives all along the Pacific coast from Alaska to Mexico.
A common northern Pacific jack, the jack mackerel is identified by the strong, bony scutes that appear all along its lateral line, which dips sharply behind the pectoral fin. Otherwise, the jack mackerel is very similar to the Mexican scad (Decapterus scombrinus), which has scutes only on the back half of the lateral line, plus a small, single finlet behind the dorsal and anal fins. The jack mackerel is sometimes misidentified as a Mexican scad because, in larger individuals, the last few rays at the rear of the soft dorsal and anal fins may be completely separate from the rest of the fin, appearing like finlets. Both fish have a dark spot on the upper rear part of the gill cover, but the Mexican scad usually has a red or orange stripe along the sides. Also, the Mexican scad usually resides farther south, from central California to the Galapagos.
Pelagic, schooling fish, jack mackerel are found from the surface to at least 600 feet. The young school in large numbers near kelp and under piers. Larger individuals -- which can reach 6 pounds -- feed on pelagic crustaceans and small fishes and may move inshore and north in the summertime. Jack mackerel may be caught on bait fished from piers as well as by salmon trollers. It's also fished commercially along the Pacific coast and canned.